1. Field of the Invention
The present invention relates to a Broadband Wireless Access (BWA) system, and more particularly to a method and a system for supporting handoff between base stations (BSs) supporting different operation profiles in a BWA system.
2. Description of the Related Art
With the development of the communication industry and because of the increased demands of users who require Internet services, conventional mobile communication systems are evolving from voice-based communication systems into communication systems which are capable of efficiently providing multimedia services such as an Internet service to users in addition to existing voice-based services. Because existing mobile communication networks were developed for primarily providing voice services, existing mobile communication networks have a disadvantage in that their data transmission bandwidth is relatively narrow and consequently service charges are typically more expensive than high-bandwidth multimedia-based communication systems.
Accordingly, research is being actively pursued to develop a communication system which is capable of solving these disadvantages and can efficiently provide Internet services. A BWA system is an example of such a system.
A BWA system is a system for synthetically providing a multimedia application service including voice, as well as various (high and/or low-speed) data and dynamic high-picture-quality images. BWA communication systems are typically known as the next generation wireless communication system and can not only connect to Public Switched Telephone Networks (PSTNs), but can also connect to Public Switched Data Networks (PSDNs), the Internet, International Mobile Telecommunication (IMT)-2000 networks, Asynchronous Transfer Mode (ATM) networks, and other data communication networks Moreover, BWA communication systems can access these networks in mobile or stationary environments based on radio media using broadband of 2 GHz, 5 GHz, 26 GHz, 60 GHz, etc., and can support a channel transmission rate of more than 2 Mbps. BWA systems may be classified into a broadband wireless local loop, a broadband mobile access network and a high speed wireless Local Area Network (LAN) according to mobility (e.g., stationary or mobile) of a terminal, communication environments (e.g., indoor or outdoor) or a channel transmission rate.
A BWA scheme has been standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standardization group, into a standard which is commonly known as the IEEE 802.16 standard. The BWA scheme of the IEEE 802.16 standard may change a bandwidth by adding channels or cells according to a subscriber' request for the bandwidth while a great many subscribers share transmission capacity including voice, images and data.
Currently an IEEE 802.16d and an IEEE 802.16e standard are being proposed and standardized. The IEEE 802.16d standard is obtained by integrating the IEEE 802.16 standard, the IEEE 802.16a standard and the IEEE 802.16b standard, and aims at providing a wireless Internet service to a stationary terminal. A goal of the IEEE 802.16e standard is to add mobility to the IEEE 802.16d standard which is applicable to a fixed BWA scheme.
As compared with a conventional wireless technology for a voice service, the IEEE 802.16e standard allows mass storage data to be transmitted within a short time due to a wide bandwidth of data and allows channels to be efficiently used due to the sharing of the channels by all users. Further, because Quality of Service (QoS) is ensured, users can use services having different QoSs according to service types and mobility of a mobile station (MS) is ensured by supporting handoff.
In an IEEE 802.16e system, in order to support handoff of an MS, a BS periodically broadcasts a Mobile Neighbor Advertisement (MOB_NBR_ADV) message to all MSs in a cell controlled by the BS, thereby reporting profile information of neighbor cells in advance. That is, when an MS in a cell moves to a neighbor cell, the MS can support handoff because it has BS information of the neighbor cell, which includes network identifiers (IDs) and channel characteristics already broadcasted from a BS.
An IEEE 802.16e communication system employs an Orthogonal Frequency Division Multiplexing (OFDM) scheme/an Orthogonal Frequency Division Multiple Access (OFDMA) scheme in order to support a broadband transmission network for a physical channel of the wireless system as described above.
In the IEEE 802.16e system as described above, it is generally defined that all BSs have the same operation profile. The operation profile includes characteristics such as bandwidths, sub-channel sizes, i.e., Fast Fourier Transform (FFT) sizes, and sub-channel operation modes. Accordingly, it is regarded that all MSs operate in the same operation profile when performing handoff.
However, in order to use various radio resources and efficiently allocate frequencies, a BS which can support various operation profiles is desirable. Unfortunately, when an MS uses a handoff support scheme in an existing communication system which supports the same operation profile in performing handoff between BSs supporting and using different operation profiles, the MS does not take notice of operation profiles of each BS. That is, because the MS cannot adequately perform the handoff between the BSs supporting the different operation profiles, problems such as call interruption may occur.
Further, the MS must combine operation profiles of a BS, i.e., a serving BS, including the MS, with operation profiles of a new BS, i.e., a target BS, to which the MS is to connect, and individually scan the combined operation profiles, in order to approach the new BS. Accordingly, the MS must frequently perform a scanning process for acquiring operation profiles corresponding to each BS. Therefore, reconnection set-up time may significantly increase. Further, the increase in set-up time may cause interruption of the connection. Therefore, it may be impossible to normally support handoff.